Bond performance of deformed rebar embedded in recycled aggregate concrete subjected to repeated loading after freeze–thaw cycles

Abstract

Freeze-thaw damage and repeated loading would degrade the performance of the concrete structures in cold regions. In this paper, 54 pull-out specimens with different recycled coarse aggregate levels (RA, i.e., 0%, 50% and 100%) were cast to exposure to freeze–thaw cycles (FTC, i.e., 0, 50, 100, 150). Next, the bond-slip curves of specimens subjected to different repeated stress ratios (0.3, 0.5 and 0.7) were tested. The effects of RA, FTC and repeated stress ratio on bond strength and peak slip were analyzed respectively. Based on damage mechanics, the bond-slip constitutive model was established, and the theoretical bond strength was calculated by using the modified cohesive-elastic ring model. The results showed that with the increase of FTCs, the bond strength of both natural coarse aggregate concrete (NAC) and recycled coarse aggregate concrete (RAC) was obviously decreased, while the peak slip exhibited an opposite law, and the RA substitution had no significant effect on bond performance due to the different cement dosages of mixtures. Furthermore, repeated loading had little effect on bond strength and slip. The damage bond-slip constitutive model was in good agreement with test results, and the bond strength calculated by the modified cohesive-elastic ring model considering stirrup pressure proposed in this paper was verified by the test data.